This box of tricks distributes the 4-20ma valve control signals from the Feedback Acquisition & Control Unit (FACU). The box takes a 24V feed in, and distributes the power and signals to one of four hydraulic valves. There is an interlock to switch the valves on, that also goes through the FACU box, so if there is a control problem or the signal cable is unplugged, the valve power is removed. There is also an output for the Manifold isolator valve.
I'm considering changing the VAPS / FACU design. Currently the FACU runs the four PID loops, and sends the 4-20ma signal for each valve down a multicore cable to the VAPS. The FACU has two connectors for the daisy chain of the data bus, and four M12 8 way connectors for each of the encoders. The idea is that the VAPS sits next to each 4 way manifold block, and the FACU is mounted on the femur of each leg, with an interconnecting signal cable between the two.
My thinking is that I should try and fit the PID control system into the VAPS unit, so it is local to the valves, then the FACU would simply be an encoder junction box. Doing this simplifies wiring between the two units, and keeps the 4-20ma signal cables very short.